<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            border: 1px solid red;
        }
        #d1{
            /*设置为绝对定位, 元素脱离文档流,后面的元素会顶上来*/
            position: absolute;
            /*相对于窗口做位置偏移*/
            right: 0;
            top: 0;
        }
        #big{
            width: 200px;
            height: 200px;
            background-color: blue;
            margin: 200px 0 0 200px;
            /*让当前元素做参照物*/
            position: relative;
        }
        #big>div{
            background-color: green;
            margin: 50px 0 0 50px;

        }
        #big>div>div{
            width: 50px;
            height: 50px;
            background-color: red;
            position: absolute;
            left: 0;
            top: 0;

        }

    </style>
</head>
<body>
<div id="big">
    <div>
        <div></div>
    </div>
</div>
<div id="d1">div1</div>
<div>div2</div>
<div>div3</div>
</body>
</html>